1. Field of the Invention
The present invention relates to a CATV (Cable Television) transmission center apparatus, a subscriber terminal device, a CATV distribution system, and a method of distributing a program, and more particularly to a CATV transmission center apparatus for transmitting programs via a CATV transmission path which is capable of bidirectional signal transmission, a subscriber terminal device for receiving programs transmitted from a CATV transmission center apparatus, a CATV distribution system which comprises a CATV transmission center apparatus and a subscriber terminal device, and a method of distributing a program, which is carried out by a CATV transmission center apparatus.
2. Description of the Related Art
In recent years, the trend in the business of CATV is toward multichannel program distribution services, and presently available CATV systems are switching from the conventional process of distributing programs in 60 channels to a new process of distributing programs in several hundreds of channels. The present invention is concerned with a technology which enables a CATV company who has been providing program distribution services with a 60-channel CATV transmission path to do services equivalent to multichannel program distribution services with the transmission facility that is presently available to the CATV.
Heretofore, it has been customary in the art of CATV program transmission to assign one program to one transmission channel.
For distributing many programs at a time, therefore, it is necessary to have as many channels as the number of programs to be distributed, and hence to maintain a transmission capacity which is large enough to accommodate those channels. To achieve more channels and larger transmission capacities, broadband transmission paths have been employed and program signals have been transmitted as digital multiplex signals.
The number of television broadcast programs that CATV companies are asked to distribute is ever increasing year after year. To meet demands for more distributed programs, CATV companies need to change the transmission facility which they presently own into a transmission facility capable of handling many channels.
The number of subscribers per optical transmission path is several hundreds at present, but tends to decrease while the number of distributed programs is increasing. In the future, it is expected that the number of subscribers per optical transmission path will be smaller than the number of distributed programs. Therefore, the number of programs which are distributed but not viewed will be increased, with the result that the cost of CATV infrastructure per program will be very high.
The multichannel program transmission requires a broadband range of frequencies, and the subscribers need to have broadband subscriber terminal devices, such as set top boxes or the like, which are dedicated to the reception of distributed CATV programs. Such broadband subscriber terminal devices add up to the cost that the subscribers have to pay to view distributed CATV programs. In addition, it is tedious and time-consuming for subscribers to select relatively few programs, which they really want to view, from many programs that are being distributed.